Manipulating matter at the nanometer scale is important for many electronic, chemical and biological advances (See Li et al., “Ion beam sculpting at nanometer length scales”, Nature, 412: 166-169, 2001). Such techniques as “ion beam sculpting” have shown promise in fabricating molecule scale holes and nanopores in thin insulating membranes. These pores have also been effective in localizing molecular-scale electrical junctions and switches (See Li et al., “Ion beam sculpting at nanometer length scales”, Nature, 412: 166-169, 2001).
Artificial nanopores have been fabricated by a variety of research groups with a number of materials. Generally, the approach is to fabricate these nanopores in a solid-state material or a thin freestanding diaphragm of material supported on a frame of thick silicon to form a nanopore chip. Some materials that have been used to date for the diaphragm material include silicon nitride and silicon dioxide. These materials are insulators, with resistivity typically greater than 1010 Ohm-cm. In contrast, silicon is a semiconductor with a resistivity less than 104 Ohm-cm, and for practical purposes can be considered to be a near short circuit in relation to the insulating diaphragm material.
Data is typically obtained from an artificial nanopore by placing the nanopore in an aqueous ionic solution of potassium chloride (KCl), commonly referred to as a “buffer” solution, the solution containing molecules of a polynucleotide such as double-stranded DNA. See, for example, “DNA molecules and configurations in a solidstate nanopore microscope,” by Jiali Li, Marc Gershow, Derek Stein, Eric Brandin, and J. A. Golovchenko, Nature Materials, Vol. 2, September 2003, pp 611-615, which is incorporated herein in its entirety by reference. FIG. 1b from that reference is reproduced herein as FIG. 1. With reference to FIG. 1, during use a voltage V is applied across the nanopore by electrodes located in the “Cis” and “Trans” volumes, and the resulting current is measured as an “Ionic current signal.”
Communication between the inventor and the authors of the above reference revealed that a problem with the use artificial nanopores fabricated to date has been high photosensitivity, necessitating taking data in the dark. Therefore an approach is needed which provides low photosensitivity. It is also desirable to minimize noise and drift in the ionic current signal.
Other investigators have proposed building nanopores in semiconducting membranes with surface insulators on the semiconductors. See, for example, U.S. Pat. No. 6,413,792, “Ultra-fast Nucleic Acid Sequencing Device and a Method for Making and Using Same,” and associated world filings WO01/81908 and WO01/81896. However, because the semiconductor in such a membrane provides a near short circuit in comparison to an insulator, the characteristics of the resulting ionic current signal are severely degraded if such a semiconducting membrane is used in the apparatus shown in FIG. 1
These and other problems with the prior art processes and designs are obviated by the present invention. The references cited in this application infra and supra, are hereby incorporated in this application by reference. However, cited references or art are not admitted to be prior art to this application.